Enhanced susceptibility to suicidal death of erythrocytes from transgenic mice overexpressing erythropoietin

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 293; no. 3; pp. R1127 - R1134
• Main Authors: Foller, Michael, Kasinathan, Ravi S, Koka, Saisudha, Huber, Stephan M, Schuler, Beat, Vogel, Johannes, Gassmann, Max, Lang, Florian
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.09.2007
• Subjects: Animals; Annexins - metabolism; Apoptosis; Buffers; Calcium - metabolism; Cell Death - genetics; Cell Death - physiology; Cells; Erythrocytes; Erythrocytes - physiology; Erythropoietin - genetics; Erythropoietin - metabolism; Erythropoietin - physiology; Female; Flow Cytometry; Gene expression; Hematocrit; Life Expectancy; Mice; Mice, Transgenic; Multiple Organ Failure - genetics; Osmolar Concentration; Phosphatidylserines - pharmacology; Physical Exertion - physiology; Polycythemia - genetics; Reticulocytes - physiology; Rodents
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00110.2007

1 Department of Physiology, University of Tübingen, Tübingen, Germany; and 2 Institute of Veterinary Physiology, Vetsuisse Faculty and Zurich Centre for Integrative Human Physiology, University of Zurich, Switzerland Submitted 14 February 2007 ; accepted in final form 26 May 2007 Eryptosis, a suicidal death of mature erythrocytes, is characterized by decrease of cell volume, cell membrane blebbing, and breakdown of cell membrane asymmetry with phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increased cytosolic Ca 2+ activity, which could result from activation of Ca 2+ -permeable cation channels. Ca 2+ triggers phosphatidylserine exposure and activates Ca 2+ -sensitive K + channels, leading to cellular K + loss and cell shrinkage. The cation channels and thus eryptosis are stimulated by Cl – removal and inhibited by erythropoietin. The present experiments explored eryptosis in transgenic mice overexpressing erythropoietin (tg6). Erythrocytes were drawn from tg6 mice and their wild-type littermates (WT). Phosphatidylserine exposure was estimated from annexin binding and cell volume from forward scatter in fluorescence-activated cell sorting (FACS) analysis. The percentage of annexin binding was significantly larger and forward scatter significantly smaller in tg6 than in WT erythrocytes. Transgenic erythrocytes were significantly more resistant to osmotic lysis than WT erythrocytes. Cl – removal and exposure to the Ca 2+ ionophore ionomycin (1 µM) increased annexin binding and decreased forward scatter, effects larger in tg6 than in WT erythrocytes. The K + ionophore valinomycin (10 nM) triggered eryptosis in both tg6 and WT erythrocytes and abrogated differences between genotypes. An increase of extracellular K + concentration to 125 mM blunted the difference between tg6 and WT erythrocytes. Fluo-3 fluorescence reflecting cytosolic Ca 2+ activity was larger in tg6 than in WT erythrocytes. In conclusion, circulating erythrocytes from tg6 mice are sensitized to triggers of eryptosis but more resistant to osmotic lysis, properties at least partially due to enhanced Ca 2+ entry and increased K + channel activity. cell volume; calcium channels; phosphatidylserine; apoptosis; excessive erythrocytosis Address for reprint requests and other correspondence: F. Lang, Physiologisches Institut, der Universität Tübingen, Gmelinstr. 5, D 72076 Tübingen, Germany (e-mail: florian.lang{at}uni-tuebingen.de )